This invention pertains to magnetic separation devices and more particularly to magnetic separation devices used to selectively remove magnetic bead-coated cells from tissues such as bone marrow or blood.
Depletion of cell populations from bone marrow has been mainly approached using antibodies conjugated to toxins such as ricin or with antibodies and complement to effect lysis of the target cells. These techniques have several disadvantages including difficulty in measuring the selective cell kill in the marrow, non-specific toxicity of either toxins or complement, and the necessity to prepare large amounts of complement. In addition, many antibodies are neither cytotoxic with complement nor toxin conjugates.
Polymeric microspheres conjugated to antibodies have been used to probe the cell surface for receptor sites using scanning electron microscopy. Molday et al., 64 J. Cell Biol. 75-88 (1975). Iron-containing polymeric microspheres tagged with fluorescent dyes conjugated to antibodies were used to separate red blood cells and lymphoid cells by binding the antibody-microsphere to selected cells and exposing the cell population to a magnetic field. Over 99% of the bound cells were attracted by the magnet. Molday et al., Application of Magnetic Microspheres in Labelling and Separation of Cells, Nature 268:437-8 (1977). Treleaven et al., Removal of Neuroblastoma Cells from Bone Marrow with Monoclonal Antibodies Conjugated to Magnetic Microspheres, Lancet 1:70-3 (1984), used monoclonal antibodies bound to magnetite containing polystyrene microspheres to separate tumor cells from bone marrow. U.S. Patent No. 4,230,685 to Senyel et al. discloses a magnetically responsive microsphere having Protein A on the outter surface. U.S. Pat. No. 3,970,518 to Giaever discloses small magnetic particles coated with an antibody layer that are used to provide large and widely-distributed surface area for sorting out and separating select viruses, bacteria and other cells from multi-cell, bacteria or virus populations. U.S. Pat. No. 4,018,886 to Giaever discloses small magnetic particles that are used to provide large and widely-distributed surface area for separating a select protein from a solution to enable detection thereof when present in low concentrations. The particles are coated with a protein that will interact specifically with the selected protein.
Recently, magnetic microspheres have been attached to target cells using monoclonal antibodies and selectively depleted from bone marrow with high energy magnets in a flow system using magnetic chambers. The technique is promising and has the advantage that physical cell removal is easier to assay than selective cell death in a mixed population. However, difficulty has been encountered in use of the original design magnetic chambers, because of the necessity to clean and sterilize the chambers between patients.
The chambers also provide only a single magnetic surface for each chamber, not providing optimal use of the expensive high-energy magnets. Thus, a device in which a disposable container contacts the marrow being depleted is an advantage. Another improvement needed is a device which allows use of more than 1 side of the magnet. Finally, a device is needed in which a directed high-energy field is concentrated on the cells passing through the flow system, to ensure removal of cells having a small magnetic moment due to attachment of a single bead, or single unattached beads. In the currently employed flow system, a very expensive electromagnet is used for the latter purpose.